Such apparatus is known, for example, for German Patent Specification No. 27 59 966.
Such prefabricated forms have since become differentiated into lighter formwork and heavier formwork. The lighter formwork is frequently termed "housebuilders' formwork", by which concreting can be carried out to heights of up to 300 cm. Residential rooms also have heights of about 200 cm, so that a 300 cm formwork height is rather exceptional. There is also industrial and civil engineering formwork, with which, of course, lower heights can also be formed, but with which heights of up to 10 meters can be achieved, corresponding to the higher structures in industry and civil engineering.
Housebuilders' formwork is usually lighter than industrial and civil engineering formwork. The former weighs approximately up to 40 kg/m.sup.2 and the latter on average is above this fixture. The differences in weight arise from the fact that, in the one case, the profile frame and transverse members are less stiff and the formwork panel is somewhat thinner than in the other type. The differences can also be recognized in the size and weight of the formwork locks. A formwork lock for housebuilders' forms has a weight of the order of 1 kg, whereas a formwork lock for industrial and civil engineering formwork is of the order of 3 kg in weight.
The formwork locks are castings or they may be welded from steel plate. The profile frames are closed hollow profiles, which are extruded from aluminum or, much more frequently, are cold-rolled steel profiles.
For such forms, a quality criterion is what formwork pressure they can withstand. Concrete is almost exclusively the material formed, and the wet concrete produces the formwork pressure. West German Standard DIN 18 216 provides information about how the formwork pressure increases as a function of concrete consistency and rate of concreting.
West German Standard DIN 18 202 gives planarity tolerances for surfaces of walls. They are listed under item 2. Of course, no form can give an absolutely flat wall. The form will, of course, tend to bulge rather more at the bottom due to the pressure increase with height. Formwork manufacturers aim to supply forms that as far as possible come within the highest accuracy class, without sacrificing essential requirements, such as flexibility, weight, simple construction, etc.
The bending deflections are related to the intervals between measuring points. If the measuring points are 1 meter apart, then the unevenness may only be 3 mm to meet the most exacting requirements.
Hitherto, the highest loadings of industrial and civil engineering formwork were from 40 to 80 kN/m2. It was thought that the number of anchor points and the diameter of the anchor bar and quality of material from which it was made should determine the maximum possible loading. It was through that if, for example, the Dywidag bar of material quality St 90/110 and 15 mm diameter, can accept a load of 01 kN with a safety factor of 1.75, then taking into account the concreted area of 1.52 m, a formwork press of 60 kN/m can be accepted. For a concreted area of 2.27 m, the figure was 40 kN/m.
It was also believed that the rate of concreting must depend upon such parameters. Discussions on this subject will be found, for example, in the "Algemeine Bauzeitung" ("General Civil Engineering News"), of Sept. 20, 1985.
Such prefabricated formwork, also know as element formwork, consists of formwork panels, which fit a grid having a length and width varying according to the manufacturer. There are very wide and very narrow elements. There are high elements and also shallow elements. For very many different reasons, in all these formwork panels the profile frames must be made from the same profile, regardless of whether the element is of the smallest or the largest type. The transverse members also must be made from the same profile, independently of the size of the element. The transverse members must also be provided in the same grid, that is to say, it is not possible, for example, to provide only every third transverse member for the smaller elements.
This means that the largest elements must comply with the tolerances.
In concreting, the pressure is exerted on the formwork panel from the front. Having regard to the anchor points present, this means that two adjacent frame members have a tendency to open between them a wedge-shaped gap towards the concrete, or even actually to open apart.
A quite different type of loading of such an assembly, which for example, may consist of ten formwork panels, exists at the instant at which the assembly is suspended from the rope of a crane. Due to wind, catching on an object or by oscillating forces, it may be that the panel is loaded from behind. Just the opposite tendency then occurs, namely the tendency for a wedge-shaped gap to form towards the outside or for this gap actually to open out. If this happens several times, it can occur that the formwork locks lose their grip and the assembly partly or entirely collapses. The consequences do not need to be explained further.
It is well known that other types of loading also occur, perhaps by the use of internal vibrators, the vibrating component of which is lowered into the concrete. Certainly, the vibrator should not come into contact with the formwork, but sometimes this cannot be prevented, for example, when the vibrator slips.
There are also the so-called external vibrators, which are fixed to the outside of the form and vibrate at high frequency. This type of loading is also objectionable.
The formwork panels should, of course, continue to remain in alignment, because if the tolerance is consumed by errors in alignment, then none remains for the errors caused by bending of the form.
The deflection of the formwork panel is, moreover, not determined by the panel being to a greater or lesser extent fitted at the edge into the profile frame, but instead the panel is supported on its rear face by the transverse members. When these members deflect then they exert a torque upon those arms of the frame to which they are firmly fixed (e.g. welded).
The embodiment described, has two mutually parallel frame arms, a plurality of stiff transverse members that are parallel to one another, are spaced approximately at equal intervals apart and have ends that are rigidly connected with the two mutually parallel frame arms. A formwork panel is situated against the front of the transverse members and supported by them.
The frame arms have an outer transverse surface, an internal periphery, a first slope extending along the internal periphery, which slope lies nearer to the formwork panel than to the outer transverse surface, ascends outwardly and is at a constant distance throughout from the outer transverse surface.
A first region of the frame arms possesses the outer transverse surface. A second region possesses an external bearing surface which is at least partly perpendicular to the formwork panel and adapted to bear against a bearing surface of an adjacent formwork panel. A third region extends behind the formwork panel, and a fourth region possesses the first slope and is spaced at a distance from the second region.
First regions on adjacent formwork panels are in alignment. The first and fourth regions each form a corner having an external corner surface on the fourth region, and the frame arms are elastically compressible perpendicularly to the fourth region in the region of the first slope.
Such apparatus further has formwork locks with two claws, a yoke with an inner surface, and a wedge drive for each formwork lock. The two claws have claw roots and mutually-facing regions with second slopes that cooperate with the first slopes and press adjacent frame arms towards each other and towards the yoke. A flat bearing surface is on the inner face of the yoke, against which the outer transverse surfaces of the frame arms bear in an aligning manner at least over partial zones. Projections are on the mutually-facing regions on the claw roots at the level of the corner surfaces. The projections are appreciably shorter than the length of the claws, a free space being present between the projections and the second slopes.